1. Field of the Invention
The present invention relates to a solar cell and a method for producing the same, in particular, to a solar cell using a barium silicide-based semiconductor and a method for producing the same.
2. Related Background Art
In 95% or above of conventional solar cells, semiconductors consisting of Si materials are used. However, Si has a forbidden band gap of 1.1 eV; therefore, conventional solar cells have not achieved sufficiently-high energy conversion efficiency. Moreover, having a small optical absorption coefficient, Si needs to be formed to have a thickness of 100 μm or above for photons to be absorbed sufficiently. Accordingly, such semiconductors are not suitable for the purpose of making thin solar cells.
There have been attempts to expand the forbidden band gap of silicon-based semiconductors in order to improve their energy conversion efficiency of the solar cells. In Japanese Unexamined Patent Application Publication No. 2005-294810, disclosed is a mixed crystal semiconductor thin film comprising BaSi2 doped with alkaline earth metal atoms, such as Sr atoms, Ca atoms, or Mg atoms. It is disclosed that a mixed crystal semiconductor thin film doped with Sr atoms as alkaline earth metal atoms especially has a large optical absorption coefficient, and has a forbidden band gap of approximately 1.4 eV.